gauge needle shake under boost....

[foxfan88]

Ive asked around on this but i wanted to get this to the masses for some input.

Since Ive had my car running, i notice when i get into boost, the needle has a slight shake to it, maybe a few psi from where it actually boosting. Ive also noticed it seems to be worse having just come into boost, as i dwell in boost for a sec, it seems to smooth out quite a bit (barely much shake)

Ive checked vacuum lines, used a hand vac pump and its reading correctly with my gauge (autometer) the reading on the vac pump actually has a slight shake at idle (due to cam overlap?) where the autometer reads pretty smooth. Car runs great under boost, smooth and no issues that i can tell. I am just trying to figure out if this shake in the needle is just an error source wise or if i am really getting this small flucuation in boost pressure (fast enough shake where the human eye sees multiple needles lol)

I pinched all lines and noticed nothing wrong, no oddball lines and no leaks., my car seems fine vac wise (pulls around 13 inches at idle)

My BOV and WG have their own seperate source about 2-3 inches past the TB using a 1/4 vac line.
FWIW i had a supercharger a few years ago (alot different obviously) but i never had any needle shake under boost with that, probably doesnt mean jack crap here though, this would lead my to believe the gauge is fine though... i havent messed with it (havent even had it out of the car in years)

Also thought about a boost leak, i could make a tester and pressurize the engine and maybe find something, all the couplers and pipes look fine so it would have to be in in the engine or maybe the intercooler.

I also tried hooking up my vac pump to the boost gauge, when i pumped the pump,it wouldnt even come close to holding a vacuum on the boost gauge (rose to 5 inches and dropped to zero instantly like i had nothing hooked up the pump. I dont know how  a boost guage is on the inside like if its supposed to  bleed like that.

Just tossing this out there i'm sure someone's encountered this before.

Thanks for any ideas/help

[turbofreek]

Does it bounce under vacumn to?  What kind of vac pump are you running? There could be a dozen of things causing this issue. Start with the basics and then start eliminating what you can one at a time till you have exhausted all external possibilitys

[foxfan88]

No under vacuum reading its smooth as can be with the autometer. Though like i mentioned earlier, when i hook the hand pump up to to the intake, the vaccum reading has a small shake (only when i read vaccum with the hand pump.)Ive read that can be due to an aftermarket cam, but its strange how the pump is picking it up and the autometer gauge doesnt get the shake under vacuum, just under boost.

 The pump is a "mityvac" pump from the parts store and it cost 40$

[1BadV6ThirdGen]

subscribing
have the same issue in my car, never was able to figure it out

[04mx]

I just read something on inovate forums about something simular but it was using a map.

 but they did say something about ( suction pulses )  and also using a thin tube to the gauge that will act as filter and smooth out the pulsations.


Just an idea

[foxfan88]

The tubing that goes from the gauge to the engine is a plastic 1/8 " line. What should i be looking for to possibly change it?

FWIW last night i went and drove the car, and for some odd reason it didnt shake at all really. Getting real stumped on this lol.

[turbofreek]

The tubing that goes from the gauge to the engine is a plastic 1/8 " line. What should i be looking for to possibly change it?

FWIW last night i went and drove the car, and for some odd reason it didnt shake at all really. Getting real stumped on this lol.

if you melted the shit it would be sporatic with underhood temps.  also with a crack in the plastic if you could ever fint it.  i ran rubber so it would not crack or tear.

[foxfan88]

There isnt but a few inches of thr plastic line under the hood before it Ts into a rubber line, but i will give that a try by replacing the plastic line with a rubber hose. that would let me know if something is wrong with the plastic line.,

[10secgoal]

Do you have it in a plenum, or in an intake runner ? Having it in an individual runner can cause what you are talking about. You would escentially be measuring what THAT running sees as the the intake opens and closes. Intake opens, pressure drops for a split second, then right back up. Maybe even read a little higher than boost as the intake closes and the boost backs up in the runner. Hope that's it or I just wasted a bunch of your time with an unclear answer lol. 5.0 manifolds have a vac port in one runner, hence the reason I ask.

[1BadV6ThirdGen]

Do you have it in a plenum, or in an intake runner ? Having it in an individual runner can cause what you are talking about. You would escentially be measuring what THAT running sees as the the intake opens and closes. Intake opens, pressure drops for a split second, then right back up. Maybe even read a little higher than boost as the intake closes and the boost backs up in the runner. Hope that's it or I just wasted a bunch of your time with an unclear answer lol. 5.0 manifolds have a vac port in one runner, hence the reason I ask.

hmm while my car isnt a 5.0 ford my vacum fitting is basically right at the entrance of one of the runners, im going to try tapping a hole in manifold so it centers up in the plenum to see if it changes anything

[JPM]

Is it a liquid filled gauge? I had to replace my fuel pres gauge with one that was liquid filled to stop that prob. Good luck.

[foxfan88]

The vac line isnt in an individual runner, but its on the end of the plenum.... I see that causing it but if it was, it would have shown it with the supercharger and it didnt then i remember that. the vac line for the gauge is in the same spot when i had the blower.

The gauge isnt liquid filled, i can see the liquid filled gauge helping but like i said ive SEEN this gauge hold steady boost readings with the belt driven charger, so something has had to change, eiter related to the turbo or something i messed up.

I will drive it tomorrow, last time i drove it, it didnt shake for some odd reason. I'll see if what it does the next drive i take.

[1BadV6ThirdGen]

i went back and looked at some of my old data logs and u can see how much it jumps on my car

top half of graph look at purple line for map sensor and bottom half green line is throttle possition
even with wot the map line is still all over the place


really shows up in this capture form the datalog look were the car is wot

[foxfan88]

interesting, about how much shake are you seeing on your gauge?

[1BadV6ThirdGen]

interesting, about how much shake are you seeing on your gauge?

mostly 2 psi up and down but ive seen it jump around 3 psi too

and it bounces fast as hell

[turbofreek]

mostly 2 psi up and down but ive seen it jump around 3 psi too

and it bounces fast as hell

what are you running for a bov?  any boost controller?

[1BadV6ThirdGen]

what are you running for a bov?  any boost controller?

that data log was taken with no boost controller hooked up,wastegate line was hooked to the turbo outlet,
and i had one of those knockoff turboxs type h i think it was bov's, took the bov off and tried withotu it and it did the same thing

edit heres the bov i used to run

[turbofreek]

that data log was taken with no boost controller hooked up,wastegate line was hooked to the turbo outlet,
and i had one of those knockoff turboxs type h i think it was bov's, took the bov off and tried withotu it and it did the same thing

try a different spring in the gate.  maybe bouncing with to light a spring in it.

[1BadV6ThirdGen]

try a different spring in the gate.  maybe bouncing with to light a spring in it.

i never thought of that, ive always run a 7 psi spring,and when i wanted to turn it up i hooked up a turbo xs hpmbc, and this year i installed a 1/4 inch shim ontop the spring to add some preload to get the gate to open later.

still doing it though

ill swap out to a 12 psi spring or so though

[turbofreek]

i never thought of that, ive always run a 7 psi spring,and when i wanted to turn it up i hooked up a turbo xs hpmbc, and this year i installed a 1/4 inch shim ontop the spring to add some preload to get the gate to open later.

still doing it though

ill swap out to a 12 psi spring or so though

so did it chage with the shim?  maybe its not letting the gate close all the way?

[1BadV6ThirdGen]

so did it chage with the shim?  maybe its not letting the gate close all the way?

nope same thing even wit the shim in place.
The shim would actually stop it from opening all the way i would think,
with the shim it actually should cause the gate to seat more firmly,hell i know it made the gate open a lil later

but liek i said i still had the same mount of bounce in my boost gauge

[turbofreek]

nope same thing even wit the shim in place.
The shim would actually stop it from opening all the way i would think,
with the shim it actually should cause the gate to seat more firmly,hell i know it made the gate open a lil later

but liek i said i still had the same mount of bounce in my boost gauge

no shim would make it harder for it to open, unless its binding the spring and causing the valve to open slightly.

[95turbomustang]

mine did that, I took my eletric boost controller off just to see, and it didn't do that. Mine did not do it as bad, it just vibrated, maybe the wave saw a 1/16 of a pound, it just vibrated basically. you said yours is moving over a pound if I read correctly.

[Orr89rocz]

my gauge bounces back and forth on my 1/4 mile runs several psi up and down but i thought it was from the car vibrating since its mounted to a guage pod on the dash... my logs show my map sensor has steady input.

Not sure what your problem is if the map is reading fluctuations too.